There is a significant and growing population of women who breastfeed for 5-6 months or more, and there is a need to develop a rational policy for the use of contraception in the postpartum lactating woman, both to avoid the unnecessary and possible detrimental use of contraception during lactation and to ensure adequate protection against the risk of pregnancy. The objective of this project is to develop a series of guidelines for 1) use of lactational amenorrhea as a family planning method, and 2) the timely introduction of an alternative contraceptive method. These guidelines will be a product of testing the validity of three hypotheses: 1) The combination of ovulation and a luteal phase adequate for implantation will not precede menses in the majority of lactating women, i.e., menses is predictive of fertility return during the first 6 months post-partum. 2) Other easily noted events are predictive of fertility return in lactating woemn, e.g. change in feeding pattern, especially the substitution of foods instead of breast milk, or changes in cervical mucus characteristics. 3) Prediction of ovulation in lactating women using such markers will be a theoretically efficacious natural method of fertility regulation. The following endocrinological and epidemiologic studies will be performed: 1) a prospective study of 20 non-lactating post-partum women using serum progesterone, estradiol and LH to validate the use of urinary assays for pregnanediol 3Alpha-glucuronide, estradiol 17 Beta-glucuronide and LH to detect ovulation and assess the adequacy of the luteal phase in postpartum women, and; 2) a prospective study of a cohort of 55 lactating postpartum women a) to assess the ocurrence of ovulation and adequacy of the luteal phase using the urinary assay, and b) to record easily identifiable events, or simple markers, which may serve as indicators of ovulation return. The validation study in non-lactating post-partum women will be conducted at Johns Hopkins University, Baltimore, and the prospective study of lactating women will be conducted at Johns Hopkins and St. Agnes Hospital, in collaboration with hospitals in the greater Baltimore area.